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// Copyright ©2015 The Gonum Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package gonum
// Iladlc scans a matrix for its last non-zero column. Returns -1 if the matrix
// is all zeros.
//
// Iladlc is an internal routine. It is exported for testing purposes.
func (Implementation) Iladlc(m, n int, a []float64, lda int) int {
switch {
case m < 0:
panic(mLT0)
case n < 0:
panic(nLT0)
case lda < max(1, n):
panic(badLdA)
}
if n == 0 || m == 0 {
return -1
}
if len(a) < (m-1)*lda+n {
panic(shortA)
}
// Test common case where corner is non-zero.
if a[n-1] != 0 || a[(m-1)*lda+(n-1)] != 0 {
return n - 1
}
// Scan each row tracking the highest column seen.
highest := -1
for i := 0; i < m; i++ {
for j := n - 1; j >= 0; j-- {
if a[i*lda+j] != 0 {
highest = max(highest, j)
break
}
}
}
return highest
}